POUYA-PASHA Power System Analysis Lab. Sheet No: 71

This is just a demo sheet. Do not use this sheet to submit your answers, use the sheet that comes from POUYA software LABs. Familiarity with DC Separate Exciter Motor Characteristic

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FAMILIARITY WITH Separate Exciter DC Motors Characteristics

LEARNING OUTCOMES: UPON COMPLETION OF THE SUBJECT, STUDENTS WILL:

1. Have familiarized with DC Motors Characteristics using software
2. Have acquired in-depth understanding of DC Machine analysis
3. Have acquired communication skills with others in a team environment.
4. Have acquired skills in computerized calculations

SETTINGS, OPTIONS, DOCUMENTS REQUIRED:

1. Activate PASHA: ACCESS PASHA must not be active when bringing the file.
2. All QUESTIONs will be answered by using ORIGINAL NETWORK except where it is asked to continue previous QUESTION.
3. Real Time Simulation must be used.
4. Some QUESTIONs NEEDs to refer or change to the input data of the network.
5. If a network has changed you can always retrieve the ORIGINAL NETWORK from the file.
6. Reading the provided manual and POUYA Manual will be helpful.
7. In PASHA if an input data is blank, it means zero or infinity as proper. If you asked for that enter the value.
8.Key O always brings the option menu and interrupt any ongoing calculation. Key X always brings you to previous menu.
9. Set the Step size = 1.25E-3.
10.In the practical test, a speed increase of 20% is allowed over the nominal speed. nominal value of speed is 1500 rpm.
11. Key X always brings you to previous menu. Key O always brings the option menu and interrupt any ongoing calculation.

12.Typical DC Motor Drive Topology

Separately Excited DC Motor

↓ Preparation and Initial Report

✔The following figure shows a state of a DC separate excitation motor.Voltage stability of excitation circuit terminals cause passing constant current from the circuit. Therefore, the flux of poles will be a constant value.

Figure.1 DC Separate Excitation

No-Load Test

✔ Using the Pouya software, retrieve the circuit of a separately exciting motor as explained in the manual. For this aim, after running the program and clicking on “Labs” icon on the first page, choose the “DC Machine Lab 1” and then from the “Network Name” section, run “lab.no71-all dc sep.ex motor“. Now by clicking on the specified area in figure 2 and changing the motor excitation, change the speed from 80% (1200 rpm) to 120% (1800 rpm).

Figure.2 Test Circuit in POUYA environment

✔For each excitation current, write the speed and the terminal voltage on the table below:

If (pu)

Vt (V)

N (rpm)

loading test

✔ Using the Pouya software, retrieve the circuit of a separately exciting motor as explained in the manual. For this aim, after running the program and clicking on “Labs” icon on the first page, choose the “DC Machine Lab 1” and then from the “Network Name” section, run “lab.no71-all dc sep.ex motor .

✔ Now by clicking on the specified area in figure 2 and changing the motor excitation, change the speed 100%(1500 rpm).
✔ For different values of Ia, write the voltages and rotation speed of the motor and using the Ea=Vt-RaIa equation, calculate Ea for different values of Ia.
✔(In this equation Ra is armature resistance and equals 1.15 ohm).
✔ Finally, calculate the torque using T=(EaIa)/(2 π N/60) and write it in the table below.

It (A)

N (rpm)

Vt (V)

Ea (V)

T (N.m)

Questions

1.According to motor electromechanical characteristics (W=f(Ia)), How much does the speed Changes from unloading to full load in the loading test?

About 2.72 %.

About 5.72 %.

Less than 2 %.

The speed from unloading to full load is constant.

2.For power less than 10 KW, How much is the speed and voltage of the motor terminal?

N=105 % , Vt=0.9999 pu.

N=105 % , Vt=1 pu.

N=120 % , Vt=1pu.

Motor power is always more than 10 KW. In unloading, more than 10KW power is consumed.

3.What is the right choice for an electromagnetic characteristic according to the results of a loading test?

The separately excited DC motor's magnetic characteristic is linear.

The separately excited DC motor's magnetic characteristic is linear before the saturation of the poles.

The separately excited DC motor's magnetic characteristic is non-linear, and the third order.

Depending on the motor power and its specifications, can be linear or nonlinear.

4.Which option is correct about separately excited DC motor?

Like a DC shunt motor, it is used in constant speed loads such as air vents.

Like the DC Shant motor, By loss of field, the flux of the machine is reduced, and it reaches the amount of residual flux. Therefore, the speed of the machine is dangerously high. So the loss of field protection in this motor is essential.

For heavy loads, these motors are not used because the Ia is too high and damaged.

All the items are correct.

5. Which option does the electromagnetic torque characteristic of the separate exciter DC motor correctly display? (Choose the closest option to the answer).

6. Which option does the electromechanical characteristic of the separate exciter DC motor correctly display? (Choose the closest option to the answer).

7. Which option does the mechanical characteristic of the separate exciter DC motor correctly display? (Choose the closest option to the answer).